The present invention is related to an imaging condition determining method and an X-ray CT (computed tomography) apparatus, more specifically to an imaging condition determining method for an X-ray helical scan imaging CT, and an X-ray helical scan CT apparatus.
An X-ray CT apparatus for performing helical scan imaging has imaging condition setting performed by the user prior to the imaging. The imaging condition may be set in accordance with the subject and the objective of imaging. A variety of parameters such as tube voltage, tube current, X-ray beam thickness, image slice thickness, helical pitch and so on may be set in accordance with the imaging condition. For the imaging condition selected, the exposure dose of the patient is displayed such that the operator can decide the suitability of the imaging condition (for example, see the patent document 1 below).
Patent Document 1 JP-A-2003-79611 (pp 8 to 9, and FIGS. 6 to 9)
In an X-ray CT apparatus as have been described above, if the exposure dose is not appropriate, the imaging condition is required to be revised. However it is not easy to reconfigure an alternative imaging condition consisted of a number of parameters so as to achieve the predetermined goal. In particular, the difficulty becomes increased with the cone beam characteristics elicited of the X-ray beam, along with the increase of the number of X-ray detector arrays.
In particular, when scanning with a thick beam, scan will terminate early, however the automatic control of the tube current in the direction of body axis will be unsubtle to increase the exposure dose. It is required to carefully select the thickness in accordance with the age of patient and the examination purpose.